Australia's highest court on Thursday
struck down the nation's first gay marriage law, invalidating the
marriages of more than two dozen gay and lesbian couples.

Australian Capital Territory (ACT)
lawmakers approved the marriage law in October and it went into
effect on Saturday.

Upon the law's passage, Prime Minister
Tony Abbott, whose conservative Liberal-National coalition swept into
power on September 7 on a pledge to lower taxes, filed a legal
challenge to the law, arguing that only the federal government has
the power to regulate marriage.

The High Court unanimously agreed that
the ACT's law ran afoul of the federal Marriage Act, which was
amended in 2004 to define marriage as a heterosexual union.

“The Marriage Act does not now
provide for the formation or recognition of marriage between same sex
couples. The Marriage Act provides that a marriage can be solemnized
in Australia only between a man and a woman,” the court said in a
statement.

Sydney University constitutional lawyer
Anne Twomey told the AP that the ruling means that only the federal
government has the power to legalize marriage for gay couples.

Ivan Hinton, whose marriage to Chris
Teoh will now be annulled, said that he was heartbroken but added, “I
wouldn't have missed it for the world.”